The invention relates to Medium Access Control (MAC) protocols in CSMA networks.
In prior data transmission systems, available transmission channel bandwidth may be subdivided into a number of discrete carriers. Examples of multi-carrier data transmission systems include Orthogonal Frequency Division Multiplexing (OFDM) data transmission systems, in which the carriers are overlapping and orthogonal to each other, such as IEEE 802.11a Standard based wireless systems using OFDM and Digital Subscriber Line (DSL) systems using discrete multi-tone modulation. Data transmissions in multi-carrier systems such as these encompass some number of available carrier frequencies.
In multi-node, multi-carrier systems, for example, systems that implement the IEEE 802.11a Standard, it is possible to adapt each node-to-node connection to a particular data rate; however, all the data rates of the individual carriers are the same. The channel adaptation or channel information used to modulate a body of a frame and to be applied to the frame body by a receiving node for demodulation may be provided by the transmitting node in the frame's header, which is typically transmitted at a lowest data rate. While such a mechanism for conveying channel information may be adequate for a small amount of channel information, it becomes less efficient for systems with more complex channel information requirements.
In point-to-point, multi-carrier systems such as DSL, the carriers may be configured for different bit rates based on channel characteristics. In a point-to-point application such as DSL, there is no need to provide channel information with a transmission as each DSL transceiver only communicates with one other DSL transceiver.